1. Field of the Invention
The present invention relates to an apparatus for stably supplying a constant amount of abrasives, and more particularly, to an apparatus that is adapted to a blasting machine or a shot peening machine (hereinafter, simply referred to as a “blasting machine”) for ejecting a mixed fluid composed of compressed air and the abrasives from a blasting gun provided with a nozzle so that the amount of the abrasives ejected from this blasting gun is controlled to a constant amount.
2. Description of the Related Art
In a blasting machine for ejecting the abrasives together with compressed air, any variation in the ejected amount of the abrasives results in a change in the amount to be processed, leading to variations in processing accuracy. In order to prevent these variations, there is proposed an apparatus for merging a predetermined amount of the abrasives per unit time with compressed air that is ejected from a blasting gun so that the ejected amount of the abrasives always becomes constant.
As one example of such an apparatus, a known apparatus for use with a suction blasting machine will be described with reference to FIGS. 5 and 6. Referring to FIG. 5, a known type of apparatus 1 for use with a suction blasting machine, as described above, includes in a blasting gun 40 a flow channel 41 for compressed air and a branch channel 42 branching off this flow channel 41. When high-pressure compressed air is introduced into the flow channel 41, negative pressure (suction force) generated at this time causes some abrasives to be sucked through the branch channel 42 and to be ejected together with the compressed air. This known type of apparatus 1 for use with the suction blasting machine includes a transport path 11 for the abrasives, which is a branch channel merging with the flow channel 41, an abrasive tank 10 communicating with this transport path 11, and means for transporting and supplying a constant amount of the abrasives in the tank 10 per unit time to the transport path 11.
As the means for transporting a predetermined amount of the abrasives in the tank 10 per unit time to the transport path 11, a drum 20′ having a plurality of V-shaped measuring grooves 23 formed on an outer circumferential surface thereof is embedded into the abrasives in the tank 10 such that a part of the outer circumferential surface is exposed from the abrasives. The drum 20′ is rotatably housed in this embedded state. Furthermore, one end 11a of the transport path 11 is arranged so as to face the measuring grooves 23 on the outer circumference of the drum 20′ exposed from the abrasives. When the drum 20′ rotates, the abrasives collected in the measuring grooves 23 is sucked into the transport path 11, merged with compressed air flowing in the flow channel 41, and is ejected from the tip of the blasting gun 40.
As a result, by controlling the rotational speed of an electric motor 30 which rotationally drives the drum 20′ by the use of, for example, an inverter, the amount of ejected the abrasives can be adjusted in such a manner that the number of times that the abrasives is collected and transported per unit time follows a change in the rotational speed controlled by the inverter (refer to Japanese Unexamined Patent Publication No. H9-38864).
Referring now to FIG. 7, to adopt the apparatus for supplying a constant amount of the abrasives for use with a direct-pressure blasting machine, a drum 20′ having many bottomed measuring holes 21′ for measuring a constant amount of the abrasives per unit time, formed on the outer circumference thereof, is disposed in a tank 10. Then, the opening at one end 11a′ of a transport path 11′ for the abrasives is arranged to face the measuring holes 21′ provided on this drum 20′. Furthermore, the other end of the transport path 11′ is made to communicate with a compressed-air flow channel 41 in which compressed air to be ejected from the front-end nozzle of a blasting gun (not shown) flows. Furthermore, the transport path 11′ is provided with a conduit 43 into which compressed air is introduced, so that compressed air introduced into the transport path 11′ through this conduit 43 is forced into the measuring holes 21′ and blows up the abrasives collected in the measuring holes 21′, thereby causing the abrasives to merge with the compressed air flowing in the compressed-air flow channel 41. In this manner, a constant amount of the abrasives merged with compressed air can be ejected per unit time from the blasting gun.
As with the apparatus for the suction blasting machine, the apparatus 1 for this direct-pressure blasting machine is constructed such that the amount of the abrasives ejected from the blasting gun can be adjusted by controlling the rotational speed of a motor that drives the drum 20′ by the use of, for example, an inverter (refer to Japanese Unexamined Patent Publication No. H11-347946).
For measuring holes used to measure the amount of the abrasives, there is also proposed an apparatus for allowing the abrasives to be collected via through-holes, instead of the bottomed holes described in H11-347946, formed so as to penetrate a disc in the thickness direction thereof (refer to Japanese Unexamined Patent Publication No. H10-249732).
In the known apparatus 1 with the above-described structure, as well as the apparatuses 1 described in H9-38864 and H11-347946, the amount of the abrasives is measured by means of the bottomed measuring grooves 23 or the measuring holes 21′ formed on the outer circumference of the drum 20′. However, extremely high processing accuracy is required to form the measuring grooves 23 and measuring holes 21′ on the entire circumference of the drum 20′ such that they have a uniform height at any position. Thus, errors in formation of the measuring grooves 23 or the measuring holes 21′ generated during processing directly lead to errors in the amount of the abrasives measured.
In addition, as shown in H11-347946 in particular, when the measuring holes 21′ are formed as relatively deep, bottomed holes, the abrasives does not easily enter the holes, thus causing the amount of the abrasives collected in the measuring holes 21′ to vary from hole to hole. What is worse is that not all amounts of the abrasives, once collected in the measuring holes 21′, can be blown out even with compressed air. This makes it impossible to ensure that a constant amount of the abrasives is collected in each of the measuring holes 21′ or that a constant amount of the abrasives is acquired from each of the measuring holes 21′.
In contrast, the apparatus 1 for supplying a constant amount of the abrasives described in H10-249732 includes measuring holes for measuring the amount of the abrasives in the form of through-holes that penetrate a disc-shaped member in the thickness direction thereof. In this apparatus 1, therefore, the measuring holes that are formed can be endowed with a constant depth (length) by making the thickness of the disc constant and, furthermore, can easily introduce the abrasives thereinto and blow out the abrasives therefrom compared with the above-described bottomed holes.
However, even if substantially no variation in the amount of the abrasives can be seen among the measuring holes, an insufficient amount of the abrasives may be collected in the measuring holes. Furthermore, even if a required amount of the abrasives is collected in the measuring holes, the abrasives may fall out from the measuring grooves 23 or the measuring holes 21′ before the abrasives collected is transported to the transport path 11 (11′), thus failing to ensure with the above-described conventional structure that the amount of the abrasives that has reached the transport path 11 (11′) is always constant.
It is proposed, also with the above-described conventional structure, that vibration be applied to the tank 10 or the drum 20′ to allow the abrasives to be easily collected in, for example, the measuring grooves 23, thus preventing a situation where an insufficient amount of the abrasives enters the measuring grooves 23 or the measuring holes 21′, and to allow excess the abrasives heaped above the level of the measuring grooves 23 to be shaken off (refer to H11-347946). When the tank 10 is to be vibrated in this manner, the abrasives is compressed hard and clumps together in the tank 10 depending on, for example, the material of the abrasives, which may undesirably decrease the fluidity of the abrasives.
Furthermore, when vibration is applied to the tank 10 or the drum 20′ as described above, some abrasives that have been collected in the measuring grooves 23 may be shaken off. This means that applying vibration as described above does not always ensure the desired performance of supplying a constant amount of the abrasives.
In addition, in the known apparatus 1 for supplying a constant amount of the abrasives with the above-described structure, a slider 27 provided at the edge of the opening of the transport path 11′ is slidably in contact with the outer circumference of the drum 20′ to prevent the pressure in the transport path 11′ or the flow channel 41 from leaking into the tank 10. For this reason, both the drum 20′ and the slider 27 become seriously worn and need to be replaced frequently. In particular, since the above-described slider is made of relatively expensive boron material, frequent replacement of the slider leads to extremely high operating costs.
Furthermore, when the abrasives to be transported is delivered into the tank 10 and is left in a lump, the abrasives may aggregate and become hard over time. This aggregation significantly decreases the fluidity of the abrasives.
If this aggregation occurs, it becomes difficult to collect the abrasives in the measuring grooves 23 or the measuring holes 21′, making it more difficult to accurately measure the amount of the abrasives. Consequently, the amount of the abrasives supplied to the blasting gun is subjected to variation.
In particular, the abrasives to be used may be an elastic abrasives produced by forming an elastic base material having abrasives grains compounded and dispersed therein into a predetermined grain size or an elastic abrasives produced by carrying, e.g., depositing abrasives grains on a surface of the elastic base material formed into a predetermined grain size. Such elastic abrasives are more easily subjected to aggregation as described above, compared with normal abrasives. Consequently, when blasting is started or resumed after the abrasives has been left in the tank for a relatively long period of time without allowing the abrasives to flow, the amount of the abrasives supplied becomes unstable or supplying the abrasives itself may become impossible in an early stage after the blasting has been started or resumed.
To prevent such failing supply of the abrasives, the following extremely time-consuming procedures need to be performed. That is, the elastic abrasives remaining in the tank of the blasting machine is completely removed when the blasting machine is to be stopped for a certain period of time, for example, at the end of the working day. Then, when the blasting machine is to be started again, the tank of the blasting machine is refilled with the abrasives before working is resumed.
The fluidity of the abrasives changes according to the grain size. Consequently, if the grain size of the abrasives is so small that relatively high fluidity is provided, the amount of the abrasives that is introduced into the tank 10 increases, thereby causing the amount of the abrasives in the tank 10 to become higher. On the other hand, to prevent this from occurring as far as possible, vibrators (not shown) are provided to apply vibration to the above-described known tank and a recovery tank (not shown). In this case, the vibrators that apply vibration to the above-described recovery tank are adjusted. This adjustment is so difficult that if adjustment causes the fluidity to decrease, the abrasive level in the tank 10 decreases. Furthermore, an aggregation phenomenon as described above may occur at the branch channel 42 (the transport path 11), causing the abrasive level to become seriously unstable.
In the above-described known apparatus for supplying a constant amount of the abrasives provided with for example, a drum that is not entirely covered or embedded with the abrasives but is partly exposed from the abrasives, the partial embedment state of the drum into the abrasives changes as the amount of the abrasives in the tank 10 changes (e.g., decreases), thereby inducing a change in the manner that the abrasives is collected in the measuring grooves 23, thereby the amount of the abrasives to be supplied is increased. For example, when the drum is disposed relatively deep in the abrasives, some abrasives may adhere around the measuring grooves 23, and such abrasives around the measuring grooves 23 may be supplied along with the abrasives in the measuring grooves 23. If this is the case, a change in the amount of the abrasives supplied will be induced according to a change in grain size of the abrasives to be supplied.
In order to overcome this problem, in the known apparatus for supplying a constant amount of the abrasives with the above-described structure, the grain size of the abrasives to be used needs to be taken into consideration to accurately control the amount of the abrasives supplied, which requires complicated adjustment.
Any apparatus for supplying a constant amount of the abrasives with the above-described conventional structure is constructed so as to arrange drums or discs for measuring the amount of the abrasives partly embedded with the abrasives and partly exposed from the abrasives as described above, so that the portions exposed from the abrasives function to recover the abrasives collected in the measuring holes or the measuring grooves. For this reason, when a constant amount of the abrasives is to be supplied to a plurality of blasting guns simultaneously, a plurality of the above-described apparatuses for supplying a constant amount of the abrasives needs to be provided according to the number of blasting guns. Alternatively, the above-described tank may be shared. In this case, however, the number of above-described drums and discs housed in the tank that need to be prepared is the same as the number of blasting guns. This increases the number of components and causes the size of the blasting machine to increase.
In view of these circumstances, the present invention is conceived to overcome problems associated with the above-described conventional techniques. A first object of the present invention is to facilitate introduction of the abrasives in measuring holes. A second object of the present invention is to make the abrasives in the measuring holes be taken out easily. A third object of the present invention is to prevent a change in the amount of the abrasives in the measuring holes while the abrasives are being moved to the transport path. Thereby, a fourth object of the present invention is to accurately transport the measured amount of the abrasives. A fifth object of the present invention is to ensure satisfactory fluidity to achieve supply of a constant amount of the abrasives that is easily subjected to aggregation as described above, for example, the above-described elastic abrasives. A sixth object of the present invention is to supply a constant amount of the abrasives irrespective of a change in the amount of the abrasives in the above-described tank 10 resulting from a change in grain size of the abrasives. A seventh object of the present invention is to provide an apparatus for supplying a constant amount of the abrasives for a blasting machine that can supply a constant amount of the abrasives to a plurality of blasting guns simultaneously.